According to the present invention an anion is recovered from an aqueous liquid, such as acetate from an acetate-producing fermentation broth, by extraction with an ion exchange non-aqueous liquid. The present invention is particularly advantageous for extracting anions from fermentation broths since fermentation which produces, for example, acetic acid, is limited because the accumulated level of acetic acid inhibits further biological production.
Many fermentation processes also result in decrease in production of the desired anion when pH change due to fermentation is sufficient to inhibit the organisms.
One method which may be utilized to remove the anion (such as acetate) is to extract it from the fermentation broth using an extraction solvent which takes advantage of solubility partition coefficients. This, however, has inherent inefficiencies since the anion must be first converted to a species soluble in the non-aqueous extraction liquid, which is usually accomplished by altering the pH of the fermentation product.
Other methods involve removal of the fermentation product, such as citric acid, by a membrane separator, which can be slow and involves specialized membrane technology.
If the fermentation product such as acetate, is to be used as a feed for a chemical process, another way of removing the anion is to add the other reactants of the chemical process directly to the fermentation broth. For example, dolomitic lime might be added directly to a fermentation broth containing acetic acid to make CMA. This, however contaminates the fermentation broth. Therefore, by direct addition of lime to the broth either the culture cannot be used in a continuous manner or the fermentation broth must be continuously replenished
However, it is not believed that a method has been heretofore known for removing anions from an aqueous liquid, such as a fermentation broth, in a continuous manner by using an ion exchange liquid for extraction, whereby the anion is extracted from the fermentation liquid in a continuous manner, then back-extracted from the ion-exchange liquid and used directly as a starting material for a chemical process. The present invention provides such a method and, additionally, has the advantageous features of neutralizing the acid produced in the broth with hydroxyl ion to produce water. Furthermore, by back-extraction, direct contact of the chemical reactants (lime) with the broth is avoided, thereby minimizing undesirable perturbations of the extraction process from the broth.